1. Field of the Invention
The present invention relates to an optical pickup apparatus enable to read two or more kinds of recording medium having different reading wavelengths such as a compatible optical pickup apparatus for DVD/CD, and particularly relates to an optical pickup apparatus using a semiconductor laser element formed of a one-chip laser diode for emitting two laser beams having different wavelengths.
2. Description of the Related Art
Conventionally, a DVD/CD compatible reproducing apparatus for sharing an optical pickup of a CD reproducing apparatus and a DVD reproducing apparatus has actively been proposed. The applicant has also proposed an optical pickup apparatus enabling to reproduce both the DVD and CD, which is disclosed in JP-A-10-255274, so that these configurations and operations will be described briefly referring to FIG. 18.
An optical pickup apparatus comprises a first light source 10 for emitting a laser beam having a wavelength (780 nm) most suitable for an information reading from a CD, a first driving circuit 11 for driving the first light source 10, a second light source 14 for emitting a laser beam having a wavelength (650 nm) most suitable for an information reading from a DVD, a second driving circuit 15 for driving the second light source 14, a first beam splitter 12 for reflecting the laser beam emitted from the first light source 10 and transmitting the laser beam emitted from the second light source 14, a second beam splitter 13 for transmitting the laser beam reflected or transmitted by the first beam splitter 12 and reflecting a laser beam reflected by an optical disk 18 to guide the laser beam to a photodetector 20 through a condenser lens 19, an objective lens 16 for gathering the laser beam reflected or transmitted by the first beam splitter 12 on an information recording surface, an information data reproducing circuit 21 for generating an electrical signal with a level corresponding to the quantity of light of the light applied to the photodetector 20 to output the signal as a reading signal, a disk determination circuit 22 for determining a kind of the optical disk 18 based on a size of a beam spot formed at the time of applying a laser beam to the optical disk 18 to output a signal of the kind, and a controller 23 for selectively driving the first and second light sources 10, 14 based on the signal of the disk determination circuit 22.
In FIG. 18, the first light source 10 emits the laser beam (shown by a broken line) having the wavelength (780 nm) most suitable for the information reading from the CD according to a driving signal from the first driving circuit 11 and applies the laser beam to the first beam splitter 12. The first beam splitter 12 reflects the laser beam from the first light source 10 to guide the reflected light to the second beam splitter 13.
On the other hand, the second light source 14 placed at a 90° angle with respect to the first light source 10 emits the laser beam (shown by a solid line) having the wavelength (650 nm) most suitable for the information reading from the DVD according to a driving signal from the second driving circuit 15 and applies the laser beam to the first beam splitter 12. The first beam splitter 12 transmits the laser beam from the second light source 14 to guide the laser beam to the second beam splitter 13.
The second beam splitter 13 guides the laser beam supplied through the first beam splitter 12, namely the laser beam from the first light source 10 or the second light source 14 to the objective lens 16. The objective lens 16 gathers the laser beam from the second beam splitter 13 at one point to use the laser beam as information reading light and the light is applied to an information record surface of the optical disk 18 rotated and driven by a spindle motor 17.
The laser beam from the first light source 10 (shown by the broken line) is gathered by the objective lens 16 so as to focus on an information recording surface C of the optical disk 18. Also, the laser beam from the second light source 14 (shown by the solid line) is gathered by the objective lens 16 so as to focus on an information recording surface D of the optical disk 18.
The reflected light occurring by applying information reading light from the objective lens 16 to the optical disk 18 passes through the objective lens 16 and is reflected by the second beam splitter 13, and a beam spot gathered by the condenser lens 19 is applied to the photodetector 20. The photodetector 20 generates the electrical signal with the level corresponding to the quantity of light of the applied light and supplies the signal to the information data reproducing circuit 21 and the disk determination circuit 22 as a reading signal.
The information data reproducing circuit 21 generates a digital signal based on the obtained reading signal and further performs demodulation and error correction to the digital signal and reproduces information data. The disk determination circuit 22 identifies a kind of the optical disk 18, for example, based on a size of a beam spot formed at the time of applying a laser beam to the optical disk 18 and supplies the kind to the controller 23. According to the disk identification signal, the controller 23 controls any one of the first driving circuit 11 and the second driving circuit 15 in order to selectively bring about a drive state.
The controller 23 drives only the first driving circuit 11 when a disk kind signal indicating the CD is obtained from the disk determination circuit 22. Therefore, the laser beam emitted from the first light source 10 is applied to the optical disk 18 through the optical system comprising the first beam splitter 12, the second beam splitter 13 and the objective lens 16. Also, only the second driving circuit 15 is driven when a disk kind signal indicating the DVD is obtained from the disk determination circuit 22.
Therefore, the laser beam emitted from the second light source 14 is applied to the optical disk 18 through the optical system comprising the first beam splitter 12, the second beam splitter 13 and the objective lens 16. That is, the first light source 10 for generating the laser beam having the wavelength most suitable for the information reading from the optical disk 18 with a relatively low recording density as the CD and the second light source 14 for generating the laser beam having the wavelength most suitable for the information reading from the optical disk 18 with a high recording density as the DVD are provided, and the light source is selectively driven corresponding to the kind of the optical disk 18 targeted for reproduction.
As described above, the DVD/CD compatible reproducing apparatus requiring two light sources requires a mixing prism to increase a cost compared with an optical pickup apparatus having one light source and also, when the first light source 10 is applied from one side of the first beam splitter 12, it is necessary to apply the second light source 14 from the other side perpendicular to the first light source 10 and thus, there was a problem that space for placing an optical system widens and the optical pickup apparatus jumboizes.